How can I express my guilt?

So I (f18) struggle a lot with keeping my agreements. I often promise my boyfriend (m18) things, for instance something we plan on doing together. But then I often change my mind, make other plans and so on. Basically I disappoint him often. I feel guilty for doing this and being this way, but I struggle a lot to express this guilt towards him. How do you do it? My guilt is very internalized and it would help both me and my boyfriend to get over my mistakes if I could communicate/express when I feel guilty.