Random depression?

im 18 and live a good life with a great loving girlfriend who ive been with for 3 months. we've shared a lot of great memories together and just click, i always thought we had a fairy tale relationship and any problem i had, i addressed with her and we fix it (and vice versa) though now i just hit a wall. These past few days..maybe last couple of weeks when im around her i just randomly get depressed and breakdown..she always tries to cheer me up and its awesome that she reures me that she'll always love me..we havent found a solution to it yet but she suggested therapy..the only possible factors i can think of are: my poor sleeping habbits (usually sleep at 3am and wake up at noon this summer), just a constant wanting to be with her every moment (its magical), or a subconscious insecurity about something. i may go through with the therapy because ill do anything to get the relationship back on track..im just scared that the therapist might randomly suggest a seperation =/