Please provide some more details, what is the state of thal in your bf, is he minor, intermedia or major. Also, have you tested to confirm that you are not thal or carry the minor genes. This can only be determined through electrophesis test.
Blood type has no bearing on thal, so don't worry about it.
As a general rule, marriage between two thal minor has 25% chance they have a thal major child.
More details would be helpful.