The thing is that if he’s having a party without inviting you over, he’s not that into you. I can understand how you would feel rejected, but cheating on him because you’re being rejected, isn’t going to help. In fact, it hurt him and you!
And if you have trust issues — it’s normal for guys to be turned off by them. Trust issues usually make people needy, insecure and they act out, like you did — to hurt someone else, as a preemptive strike. It’s a very destructive, and it would be a good idea to focus on those and see if you can work through them and understand why you have them and how to overcome them.
And finally, if you see him kissing a girl on social media, texting all day isn’t going to make you seem attractive to him. It’s going to push him away…. which is what is happening. If he’s not responding, and doesn’t want to see you… the best thing you can do is accept the rejection and move on.
I hope that helps.