Trust me bro, it’s completely normal. After reflecting on myself the past few years I’ve realized that I am actually really insecure, and it caused a fair amount of arguments. But I’d say it’s a big red flag either way, to me I think it shows a lack of self respect and it portrays weakness. You were literally just in a committed relationship with someone , only exclusive with them... And then you go and intentionally find someone to have sex with , On tinder , yeah not okay... Sorry to make you think about it any more than you already do but desensitization isn’t the key to getting over a heartbreak. It’s more about realization and then the detachment process. I also got burned by a girl I lost my virginity too, so I know exactly how it feels. &amp; they just act dumbfounded about it like the same thing didn’t already happen to them in the past... It’s completely normal what you’re going through , don’t beat yourself up and although I HATED hearing this, it’s true - there are literally millions of women out there that I promise you’d find just as attractive if not more. And many of them are probably capable of treating you much better. With that being said , just chalk this one up as a loss and focus on making sure you’re ready for the next person. Completely forget about that girl, but just don’t be surprised that when you do - she’ll probably come running back like a puppy. 
When she does, don’t be a sucker - let her hear shit how it is. People tend to not take you serious in relationships until you show them you’re not playing games, but it’s too late for that. Don’t be the type of dude that lingers around out of weakness during times of irrational behavior. Show her the man you are and that you’re capable of getting something new just like you got her, but Someone that’s worthy of your time and respects you. She’s honestly probably not even into her new dude , she’s with him to get over you and if he has any feelings attached at all he’ll get burned too but you never know what he’s looking for so maybe not , but shame on her for giving herself away so soon after a relationship. Gotta make you wonder if that person was ever worth it anyway.