Same-sex relationship

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In The Sims series, every Sim is technically bisexual, as he/she can have a crush on, fall in love with, engage in romantic interactions and have sexual intercourse with a Sim of either gender, provided they are of the appropriate age group(s).

There aren't any premade homosexual couples or families in the series, although some single Sims are lightly implied to be homosexual in their bios. However, all Sims aged teen and above, both premade and player-created, can engage in both heterosexual and homosexual romantic relationships. Players can also create married/joined same-sex couples in Create-A-Sim.

Possibilities for Sims in same-sex relationships

 * In The Sims, same-sex couples can cohabit but not marry. However, since marriage is not a recognised state in the game, only a brief social interaction, once a homosexual couple are living together the effects are exactly the same as for a heterosexual married or cohabiting couple. In The Sims 2 there is the option of formalising any romantic relationship, but with different titles for same-sex couples (Joint Union) and opposite-sex couples (Marriage). In The Sims 3, marriage is available to any couple in a romantic relationship, and Sims of either gender will recognise their spouse as "husband" or "wife". In both The Sims 2 and The Sims 3, same-sex couples can go steady with one another and get engaged in the same way as opposite-sex couples.
 * All the games in The Sims series allow same-sex couples to adopt children. In The Sims, all households will occasionally receive a random phone call asking them if they want to adopt a baby; since no formal relationships exist between Sims in the original game, any adults living in the household can then be regarded as the adopted baby's parents, at the discretion of the player. In The Sims 2 and The Sims 3, the Sim wishing to adopt must call the adoption agency using the Call... Services option on a telephone. If the Sim who calls the adoption agency is married/joined (in The Sims 2) or married/engaged/going steady (in The Sims 3) then their partner will be considered the co-parent of the adopted child, and receive a line on the family tree.

Problems faced by Sims in same-sex relationships

 * In the original The Sims, Sims with a romantic attachment to a same-sex Sim not already a member of their household could not ask that Sim to marry them. They could be invited to move in as a roommate, but there was no differentiation between a same-sex love interest and a platonic friend of either gender. However, since marriage in The Sims was largely informal, the effect on game-play was minimal.
 * The Sims 2 allowed formalised homosexual relationships in the form of Joint Union, identical to heterosexual Sim marriage in everything but terminology, although some players have observed that a Joint Union may yield fewer aspiration points than a Marriage for a Sim with a related want. However, numerous player-created hacks are available that allow same-sex couples to marry in The Sims 2 on the same terms as opposite-sex couples, and in The Sims 3 all couples are able to marry, regardless of gender.
 * None of the games in the Sims series allow homosexual couples to have children that are their biological offspring, although they have always been able to adopt in the same way as heterosexual couples or single Sims. However, in The Sims 2, cheats and hacks can be used to allow a same-sex couple to have a baby that is the biological offspring of one or both of them.

Premade (possibly) homosexual Sims

 * Gobias Koffi, one of the premade Sims living in Sunset Valley (the only neighbourhood that shipped with The Sims 3) is implied to be homosexual, as is his late father, Gaylord. Gobias's bio hints that he has been unable to meet the right woman because he may in fact prefer the company of his male friends. Gobias has no mother on his family tree, suggesting Gaylord may have adopted him. Both of their names also offer hints as to their possible sexual orientation: Gobias appears to be named in honour of a sexually ambiguous character from TV's Arrested Development, while Gaylord's name presents an obvious pun on the word "gay" as slang for "homosexual". If this is the case, then Gobias would be the first premade, playable homosexual Sim in the series.
 * Using SimPE or another third-party editing package for The Sims 2 allows players to view their Sims' degree of attraction to both genders, which determines how likely they are to accept or reject a romantic advance from a Sim of that gender. Players have commented that several Sims show a preference for their own gender, often despite being involved in a heterosexual romantic storyline. The most commonly cited example is that of Kent Capp, who has a slight preference for males at the beginning of the game, despite an implied budding romance with Bianca Monty.
 * At least one player has loaded the premade female character Constance Shelley in Riverview and found her to have a romantic attachment to another premade female Sim. This may be deliberate on the part of the game's creators, or may be a result of the Story Progression feature in The Sims 3, which allows Sims to (amongst other things) form romantic relationships without the input of the player. [This in itself may suggest that, unlike in the original game, Sims in The Sims 3 will default to bisexual rather than heterosexual behaviour if they are allowed to act autonomously.]