Why does it say "Dodi Li va'Ani Lo"?
Torah Temimah citing Shir ha'Shirim Rabah: He is Elokim to me - "Anochi Hashem Elokecha" (Shemos 20:2), and I am a nation to Him. He is to me a Father, Shepherd, Guard
What is the significance of "ha'Ro'eh ba'Shoshanim"?
Rashi: He grazes His flock in roses - in a good pasture, comfortable and nice.
Seforno: He tends (oversees) Tzadikim of the generations.
Malbim (Melitzah): When bodies graze to sustain and finance them, this is called Ro'eh b'Lechem uv'Mayim, and "bi'N'os Deshe Yarbitzeni" (Tehilim 23:2). When Nefashos 'graze' for their Nevu'ah and to understand His Emes, this is called grazing on roses, which give a [nice] smell, for it is spiritual grazing. Via it, the intellectual beings and Nefashos live.
Malbim (Mashal): He brought to her fragrant roses, for a remembrance of his love.