4th time father, and unplanned, in mid-40's and not sure how happy I am (I'm not).

I'm in my mid-40's, divorced and have 3 children from my previous marriage. Two are grown up and in the workforce. My daughter is starting HS next year. I live with my GF of 4+ years. She has told me that she is pregnant for the first time.

We were trying earlier in our relationship but she had fertility issues due to PCOS and I was struggling with decreased libido and impotency issues (my sperm count was half of where it should be for my age range and motility wasn't sufficient either). The clinic we were going to put us on a regimen and, if needed, suggested maybe in-vitro. Since that time, we've resigned to not getting pregnant. She has stated that if it happens...great, if not? No big deal.

As of recently, I figured, since I'm pushing 50, my impotency issues would just get worse and not better. And I've started TRT as well...so I figured there would be no need to get "the snip" and I've always felt uncomfortable suggesting it to her.

I've also been looking forward, significantly, to an early retirement and having our time to ourselves and doing whatever we choose to do with our time. At this point I'm fairly certain I do not want to go through the rearing process again...I do not look forward to being in my mid 60's when my child graduates HS...or being perceived as a grandparent to my child. And honestly, I don't have the energy. But I also do not want to deprive my girlfriend of the joy of childbirth and parenting.

Another issue is I'm very concerned about how it will psychologically affect my children from my previous marriage. At this stage..I'm more mature than I was in my 30's (we won't even discuss my 20's). I worry that they will perceive the wisdom of my mistakes as a younger father, and now knowing better and being better prepared, as favoring another child. Or even worse, as them being unwanted because it was with their mother.

Any advice or has anybody been through similar circumstances??