Just wanted to offer you some advice.

As someone who suffered from this for many years after being cheated on early in life, the trick is to not hold on so tight; to be okay on your own and treat your SO as a supplement to your life - not make your life around them (initially).

Inevitably, as years go by, this becomes harder and harder, but you should never lose yourself completely in another person - take care of yourself too and love yourself.

I poured myself into relationships and when things started getting bad, I felt like my own life was ending. It's not - love someone without getting lost in them. Take care of yourself, retain independence, and draw clear lines in the sand - don't tolerate cheating "once", or lying regularly - once someone gets away with it with you, they're just going to do it again.

Be nice about all of this - as nice as you can. If someone cheats on you, take a deep breath, remember that you are your own person - tell them that it's unacceptable to you and separate yourself. Be firm in this - there's no need to yell and scream - you should be at peace. You didn't do anything wrong. It's not your fault that someone cheated on you - it doesn't mean you're not good enough at sex or you're not good enough at anything else - it just means they are a cheater. If you refuse to be with a cheater, the course is clear.

This helped me a lot. If you're so insecure in your relationship that you can't be apart from your girlfriend, then it's a big red flag that you SHOULD be apart - take a step back and see if she runs off. If she does, you just saved yourself a ton of time. If she keeps coming back to you, you're doing it right.

tl;dr don't chase - be chased