I really don’t know what to do

My fiancé has been talking to this for weeks. He said he’s known her forever but he moved the conversation from messenger to Snapchat I guess because he didn’t want me to see what they talk about. I’m perfectly fine with him having female friends but he likes every single picture she posts on Facebook but doesn’t like any of mine and when I mentioned it to him his response was “because she’s pretty”. Friday night he invited her out for karaoke which is our thing we do every Friday night. So I got drunk and let my jealousy get the best of me. We got in a huge argument in the parking lot and then his mom took me home. He didn’t come home until Saturday morning and he says all they did was talk. But since then he’s been kind of distant and we’ve barely kissed or hugged in two days. Am I overthinking things? Should I just forgive and forget? I’ve already tried talking to him and let him know it bothers me that he’s talking to her and he doesn’t seem to care because he’s still doing it. I honestly don’t know what to do because I’m so in love with him and this whole situation makes me feel shitty and unwanted😭