Girlfriend cheated on and left me for one of my best friends

I met my ex when I was 18 and she was 19 through a mutual drinking buddy and we hit it off super fast. She was a a skinny white girl 5,10 probably 130lbs with a really nice body. We started spending every day together pretty fast and spent a lot of time with one of my good friends and his girlfriend because we all got along (I’ll name the guy Chad for the story and my Ex Lexi) .
After about 4 months I started renting a duplex with her close to her family home and that became the hangout spot pretty quickly. She never had a job and it was pretty common for me to get home and have people hanging out at the house already. Most of the time there was at least one or two girls but a lot of times it would just be Chad and a couple of his friends without his girlfriend. We would drink all the time, and Chad and his girlfriend would stay the night or sometimes just Chad . After about 5 months Lexi almost completely stopped having sex with me which was weird because we would normally have sex at least 3 times a week since pretty soon after we met. This went on for a couple of months before Chad told me he broke up with his girlfriend and really needed a place to stay. He didn’t have a job at the time but I told him he could stay with me as long as he was looking for one. Whenever I went to work they would just hangout all day. He would come with us over to her mom’s house nearby sometimes and Lexi’s sister would always flirt with him and make comments about how handsome he is which would kind of make me jealous. Me and Lexi started getting in arguments a lot around this time and sometimes I would sleep in the other room of the duplex with Lexi in our room and Chad on the couch. After about a month of this I had enough and just packed up my stuff and left her.
Chad just stayed at the Duplex with her but I couldn’t really blame him because he didn’t have anywhere else to go. A month or so after the break up I noticed Chad had me blocked on everything, Chads ex girlfriend hit me up and told me the reason they broke up is because Chad cheated on her with Lexi and Lexi also cheated on me with a couple other guys. About 6 months after the whole break up situation I saw a Facebook post from her sister that Lexi and Jacob were having a baby. I know I was stupid at the time but it turns me on so much to think about how much they must have been sneaking around behind my back and how long they were doing it for. I’m sure he would fuck her raw and cum in her all day while I was at work and probably when I would sleep in the separate room.