Beachlover, I have lost and gained the same 50-75 lbs. more times than I care to recall. In between those large gaines/losses, I have gained any variety of lbs. and lost and gained, etc. I guess I'm trying to say is that I get it. I understand the struggle. I understand the overwhelming feelings of disappointment that coincide with weight gain. However....none of those feelings are going to change anything for the better. On the contrary! It is most likely that they will cause you to gain even more weight.
The best way that I have found to deal with this type of a situation is to just let it go. Accept and love yourself for who you are and acknowledge the fact that you are more of an expert now. You know what it takes to lose those lbs. and you also know (hopefully) some of the things in life that can lead you to gain. The only thing that is useful about the past (in this case) is what you learn from it. That's it. So, pick yourself up, dust yourself off and make a commitment to stick to your plan. But here's what I do....I make an absolute commitment to just stick to my plan for a single day. Yep. That's not too terrible or overwhelming is it?
Well.....it kind of can be. Nevertheless, it IS possible and you can do it! Commit to one day and imagine yourself waking up the next morning and feeling so good about staying on track. Then? Then you do the same thing for another day and another day and before you know it, you're back on track and you start to feel empowered again. You keep that momentum going as long as possible and within some time, you realize that you're actually doing it! If you slip, repeat the above.