I've been thinking about my ex lately even though I'm now in a happier relationship.
Do you know why you are still thinking of them?
I can't get them out of my mind. I want them back in my life again.
When you are in a relationship, you should focus your attention on your current partner and not memories of your past ones. It's unfair to your current partner that you are still getting hung up on memories of your ex and wanting them back in your life. If you are having trouble moving on, you should talk to a therapist so that you can better process what happened in your past relationship and be able to stop thinking of your ex.
I feel I always need a love life to keep me busy, I do miss them quite a bit.
If you are really unable to move on, you can attempt to break up and get back if you think your current relationship won't work out. Your happiness matters a lot, and if your current one doesn't do that, your fate is in your own hands.