Only you can do this, my friend. If you want to be convinced this trade deadline was good, you're on your own, because no one will be able to do that if you have made up your mind that it sucks.
Instead, try this: don't be one of those "fans" that always has to complain about something. The team will never go 82-0 and sweep four series' in a row on their way to the cup. The Bruins are made up of, coached by, and run by human beings who will make mistakes, have bad days, and tough moments. It is what it is. Enjoy the game of hockey. Support the team we have, look for the good in it all and, stop finding things to criticize or speculating about what might have been or what might happen.
There are plenty of things to be disappointed by- a 9-3 loss to the Canucks, losing game 7 to the Blues, the coaching tenure of Dave Lewis, the Jumbo trade, etc. Be disappointed and then dust it off and get ready for the next game