Broke up from a 20+-year relationship at age 45 and it has been very interesting. I dropped a couple of friends and put more effort into looking for new activities. My children are now 17 and 19, so the separation has coincided with them becoming more independent, giving me more time to do my own thing. But I realise now that I could have done more for myself before. Maybe you culd also start doing some things for yourself, before you even leave?
My breakup was difficult, so part of the excitement might have been that I was dealing with big feelings (and depression) - but it was really like I had forgotten who I was, and rediscovered myself. I had forgotten what it was like to be starting out on new projects, meeting new people as myself, not part of a couple. I did some therapy and worked through some problems I've always had with low self-esteem and anxiety. Not something that goes away overnight but it has given me something to work with.
I've tried out rambling, dancing, keep fit, and meeting up with some social groups to do stuff like board games or cooking. The one new activity that has stuck strongest has unexpectedly been improv theatre, which turns out to be a good way to practice a more positive, take-it-as-it-comes outlook to life :)
I'd only ever been with my husband, really, so was quite keen to do a bit of dating. Not looking for anything long-term as I'm still quite keen to gain more experience :D and don't have time what with the activities - but I have now had a couple of other partners and have gained a bit of confidence on that front having got some nasty comments from my ex. Simply seeing that everyone wants different things in bed or from a partner, and my ex's way really wasn't the only way, has made me feel better.
I've found that there are a lot of people in their late 40s and early 50s, jangling about after their long-term relationship has broken up, looking for new things to do and new friends to do it with.