L.S.
This is tough. I have been married for 8 years and we have a blended family. Our kids felt loyalty to their other parents. While they wanted us to be happy, by letting themselves like the new person, they felt like it would be a betrayal to the other parent. The fact that it has just been you and them for the past 9 years makes it especially difficult because there is also that fear that this new man is going to replace them in your life. There is no easy answer on this and if you do get married, the children will be a point of contingency in your relationship so be sure he understands that going in. As for advice, take it slow. Understand that they are not going to love him as much as you do for a very long time. Also understand that while he will grow to love them and care about them, he will probably never have the same attachment to them that you do (side note: this can be a good thing because he can provide you with a non biased opinion during the difficult teenage years). Give the kids time individually to get to know him. Find common ground between your friend and each child and then figure out a way to incorporate it. Example, my son doesn't play sports but he loves the outdoors so, my now husband took us hiking some place we had never been. Took my son climbing and doing fun stuff that he hadn't gotten to do before. Remember, and maybe even point out to your kids, that they are not always going to be around. In a few years they are going to be grown and on their own and you will be all alone. It is time for you to have someone in your life that cares about you. Make sure they see how well he treats you and be sure they understand that he is not going to replace them in your life. You will have to have this conversation may times over the next few years before it finally sticks. Good luck. If you can get past this part, it is worth it.