I'm just wondering if I did the right thing.

Here's the story...

So my ex and I were dating for 6 months, he moved in within the first month(mistake maybe) we were so great, we had our fights thou, but always pulled through them. The last month of the relationship he started a new job, made some 'new friends' two were guys and two were females. Which one female and one guy were in a relationship.. the only female was supposedly a 'hardcore' lesbian(she looked like it too and everything). My mom saw him and the lesbian at a park together, my mom asked him where I was; he told her I was sleeping and continued to walk with her, let me say that he told me he was going to his step dads house to help him. Once he saw that my mom saw him, so he texted me telling me his other friends and 'her' invited him to hang out... he told me he was gonna be there for 10 mins and then leave.. It ended up a HUGE fight. I seriously had a really bad feeling about this so called lesbian chick... maybe a week or two after that, my ex told me he had to get away for a week & think about some stuff, and he'll move back in and it'll be all better... well.... he avoided me the whole time he was gone, when he promised me to come see me at least a day or two.. he barely talked to me, but yet said I was the only one he wanted to be with & he loved me. Etc.... well I found out on Instagram!! That he was over at the 'lesbians' house, & her caption on the picture wasn't friendly like.. it was like 'hey I like this guy really much.' The caption was 'so much dorkyness and happiness in one picture' let me remind you; it wasn't the only picture was posted with him; and it seemed like they were a couple, and also let me say that it was A DAY before we broke up when it was all posted. & the only reason why it was a day, was cause I had plenty of people come to me and sending me the screenshots of the pictures. I confronted him, he was very rude about it, and told me I was being psychotic & called me a dumb fuck.. 😂 now since then I haven't talked to him... THEN I found out that the so called lesbian and him got into a relationship FOUR DAYS after we broke up!!!

like 2 months passed, my birthday came... he texted me saying 'happy late birthday' since it was a day after.. (which I don't understand how he remembered unless he was on my moms fb stalking) I didn't reply back to him. Was I right in this? Should I at least told him thank you? Or what? I'm asking opinions here I guess.

I was really in love with this guy, he was the first guy I opened completely up too. And the first guy moved in with me... I thought I had a future with this guy... being married to him, having kids... etc.... it hurt really bad when I found out he cheated... I'm still hurt about it.... 😔