This is a subject that is close to my heart, as a single parent, being a stepchild and having a partner with a child.
I am extremely child focused. Everything I do is centred around what is best for them. Being a single parent has been undoubtedly hard on them. I have 3, one is now 17, the other two are 6 and 4. My eldest suffered because I was unable to facilitate extra curricular activities for him, or to ferry him about to his mates etc through his teenage years. He got so little of my time, when he needed it so much more. My middle one was undiagnosed (but now is, Autism/ADHD) and my youngest was a newborn (ex husband left whilst pregnant with youngest). The younger two also suffered because they hardly got one to one time, and I just couldn't do everything I wanted to do for them as their parent. It was horrendously difficult. I was split in 3 ways. Then I had to go back to work. As a midwife. So not exactly without responsibilty.
A year later I met a lovely man. As I got to know him I knew he could bring lots of benefits to my children due to his nature. So after some months, I introduced them slowly. The youngest 2 adored him from the off. The eldest approved of my choice and was vocal about this approval in a way that reassured me he was genuine (and not trying to please me).
We are two years down the line now. My partner has more than proved his commitment to the children over this time. He runs them around to activties (even the eldest!). He brings them treats when he gets money (rare! He's a student teacher!). Both last year and this year he has attended sports day as I could not. He has made massive birthday cakes (with actual skill!) for all my children. He listens to reading and helps with homework. He looks after one so I can take the other for one to one time. He comes on trips out as he knows how difficult it is for me on my own with a child with additional needs plus a younger one.
They have all had so much more enrichment (the above are just examples, the actual list is far too long!) thanks to his presence. All of which he does willingly, and with love and care.
He has his own daughter, as a result of a 3 month dating type relationship. Her mum has made it difficult from the day she was born, cancelling contact repeatedly, calling her new partner (met when child was 6 weeks old) daddy, plastering pictures of their "perfect" family all over facebook of my partners daughter, the ex's older child and the new partners child. It ended up in mediation, which failed. It then ended up in court. He has fought to keep a strong relationship with his daughter despite the challenge her mum posed. I observed this from the sideline, and his absolute commitment to her. I am in no doubt he would leave me and put her first if that is whathe had to do (as I would for mine!)
So between us we have 4 children. We have discussed at length how we will shape our future and what we both want for our respective children. There is no doubt for us that we will both support each other's child/ren. My house will remain my house. He will pay debts (to family borrowed to pay for court) from his first few wages later this year. We will draw up wills. We will ensure we are both protected (thus our children are) going forward.
I appreciate that this is the kind of information people don't see from the outside looking in. You may think people are selfish for moving on with new partners. I definitely don't feel selfish - I am doing it to benefit my children by having more income (in the long run, but not in the short term) and more life opportunities due to an additional caring and loving adult in their life. Of course I love my partner - but the love is so much greater because of how he is with both mine and his children. It cemented my feelings for him.
As a side note - my partners dad is not his dad. My partner is 2nd eldest of 10 children. My partner and his older sibling are treated exactly the same as the younger 8 who are biologically related. A few weeks ago his dad paid for us (me, partner, all our children and himself) to go to a theme park for the weekend, paying for everything including accomodation. He wasn't blood related to a single person he paid for. He did it because he wanted to help us have a nice weekend and give us a break by having an extra adult around to help with small children.