going through a major op does make you feel weepy, depressed, take stock on life etc...
I had a major op in 2002 (all of upper bowel removed) & I had an outside poo bag (colostomy) and a year later 2003 I had another major op and had a pull through done (poo bag gone completely) I have a husband and 2 teenagers and was thankful to go back to a relatively 'normal' life but I felt 'why me' since 1998 when I first had ulcerative colitis.
Talk about being the lowest of low in mind and soul and then to be given a second chance to be with my family again was absolutely fantastic. I can see where you're coming from.
Your bf is bound to think the worst & think you're finishing with him. You need to explain exactly how you feel & that it's something you feel greatly in need of doing (travelling). There's no guarantee that you'll feel the same about him when you come back, so whatever you do, don't give him false hope. I know you feel he is the one but things can change beyond your control.
Your confidence is bound to have taken a blow, I put on a few stones after my op and I only lost a little of it but I'm happy in myself and my family which are the most important things as well as life itself.
You do what you need to do & good luck. I hope your bf is understanding or does come with you but it is a huge thing for him. Just because he doesn't come with you doesn't mean he loves you any less.
Reach to your inner self and say You survived the bombing, you've come through the op and you're still in this world. What you look like is immaterial, there are people of all shapes & sizes out there, people with disabilities, people that are starving in the world & worse off then yourself, and they cope to the best they can.
Be happy and live for the moment!
good luck x