Help me please... I just want to be happy (anyone in long-term r'ship)?

Why is it when I get closer to my boyfriend I get scared? Does that mean I have a fear of abandonment? If so, is there any way to resolve this fear? We both feel very similarly about it... I guess, we're both scared of getting hurt. Is there any way to make each other feel as though nothing is going to go wrong, and that we'll get through anything? It's like my head's interfering with my heart, and I wish it would stop because whenever I get excited about our future together, I dwell on the negative things that happen. I love him so much, and all I want is for us to be happy forever, but it just seems like when things are great I always focus on something bad that hasn't even happened but fret that it's going too. I love him so much and I don't want to ever lose what we have, is it possible to just forget about the negatives, and our fears and just be happy?