Once two Sims have established some Romantic Relationship, you can ask to be Boyfriend/Girlfriend at just 30% (1/3 of the bar). This will not likely come up just walking up to them, but if you simply pull off a few Romantic socials, the option will appear.

How do you get a Sim to be your girlfriend?

Ask the Sim to date. Once the Romance bar is at least 30 percent full, select the Romance menu option, then select Ask to Be Boyfriend or Ask to Be Girlfriend in the resulting menu. This will usually result in the Sim becoming your Sims partner.

Can you be married and have a girlfriend in Sims?

Dating, Falling in Love, Proposing Marriage, and Having a Wedding. In The Sims 3, your Sim can pursue Romantic Interests and have a girlfriend or boyfriend. They can deepen and strengthen those relationships until the Sims are in love. Sims can then propose marriage and eventually marry their fiancee.

Can you have a boyfriend while married Sims 4?

You can have multiple partners at once and even get married sims to divorce their husband/wife to marry your sim from what Ive read on the forums.