Your boyfriend might be a two-faced bastard who's balling your best mate all the way to heaven and back, but privacy remains the sacred basis of all our selfish individual freedoms.
Maybe he's completely faithful but you're still needy and anxious about his feelings. I'm sure you also access his email account, rifle his pockets and eavesdrop on his conversations.
A woman's spying is merely a symptom of her chronic sense of inadequacy, the feeling that he's too good for you and could leave at any time. And your feelings are right.
Could it be that you're not that hot and you know it? If that's the case, he'll be gone soon enough, so quit fretting and poking around in his business and simply enjoy the time you have left.
Your deep suspicion and self-loathing ultimately stems from one of the usual boring clichés that govern human behaviour. Did Daddy leave when you were little and now you can't trust men?
Whatever the issue is, you just have to find someone you can confide in, who'll listen, put his arms around you and say those three magic words that every woman needs to hear: "Get over it."