I'm not going to give my older sister's boyfriend my 'blessing'
Why are you denying him of your blessing?
I don't want to lose my sister's love
It's your right to approve of who your sister will marry but it is ultimately not up to you. If she decides to go forth with the wedding, I do hope you still attend it and try to feel happy for her even if you have reservations against her boyfriend. She will see you as more supportive and caring.
I just don't want to lose my sister away. I just do not like her boyfriend.
Well, unless you have a good reason to not like him, I feel like you're being unreasonable. You are not always going to see her boyfriend and you will still have your sister, so I think you're being afraid of something that really isn't happening. I do hope you get to know her boyfriend and soon to be husband, as you may be seeing him a lot in the future.